The present invention is directed to novel cellulase compositions and methods of use therefor in industrial processes. In particular, the present invention is related to treating textiles, e.g., laundering and processing, with a mutant cellulase derived from Thermomonospora spp. The present invention is further related to the use of cellulase derived from Thermomonospora spp. to enhance the digestibility of animal feed, in detergents, in the treatment of pulp and paper and in the production of starch and treatment of by-products thereof.
Cellulases are enzymes which hydrolyze cellulose (.beta.-1,4-D-glucan linkages) and produce as primary products glucose, cellobiose and cellooligosaccharides. Cellulases are produced by a number of microorganisms and comprise several different enzyme classifications including those identified as exo-cellobiohydrolases (CBH), endoglucanases (EG) and .beta.-glucosidases (BG) (M. Schulein, Methods in Enzymology, Vol. 160, pp. 235-242 (1988)). Current theory holds that the enzymes within these classifications can be separated into individual components. For example, microbial cellulase compositions may consist of one or more CBH components, one or more EG components and possibly .beta.-glucosidase. The complete cellulase system comprising CBH, EG and BG components synergistically act to convert crystalline cellulose to glucose. The exo-cellobiohydrolases and the endoglucanases act together to hydrolyze cellulose to small cello-oligosaccharides. The oligosaccharides (mainly cellobioses) are subsequently hydrolyzed to glucose by a major .beta.-glucosidase.
Cellulases and components thereof, used either singularly or in combination, are known to be useful in detergent compositions and for treating textiles. In the textile industry, during or shortly after the manufacture of cotton-containing fabrics, it is known to treat such fabrics with cellulase to impart desirable properties to the fabric. One purpose of this treatment is to remove fuzz, i.e., untangled fiber ends that protrude from the surface of a yarn or fabric, and pills, i.e., bunches or balls of tangled fibers that are held to the surface of a fabric by one or more fibers. Accordingly, in the textile industry, cellulase has been used to improve the feel and/or appearance of cotton-containing fabrics, to remove surface fibers from cotton-containing knits, and also for imparting a stone washed appearance to cotton-containing denims. In particular, Japanese Patent Application Nos. 58-36217 and 58-54032 as well as Ohishi et al., "Reformation of Cotton Fabric by Cellulase" and "What's New--Weight Loss Treatment to Soften the Touch of Cotton Fabric", Japan Textile News, (Dec. 1988) each disclose that treatment of cotton-containing fabrics with cellulase results in an improved feel for the fabric. It is generally believed that this cellulase treatment removes cotton fuzzing and/or surface fibers which reduces the weight of the fabric. The combination of these effects imparts improved feel to the fabric.
Clothing made from cellulose fabric, such as cotton denim, is stiff in texture due to the presence of sizing compositions used to ease manufacturing, handling and assembling of clothing items and typically has a fresh dark dyed appearance. One desirable characteristic of indigo-dyed denim cloth is the alteration of dyed threads with white threads, which gives denim a white on blue appearance. For example, after a period of extended wear and laundering, the clothing items, particularly denim, can develop in the panels and seams localized areas of variation in the form of a lightening in the depth or density of color. In addition, a general fading of the clothes, some pucker in seams and some wrinkling in the fabric panels can often appear. In recent years such a distressed or "stonewashed" look, particularly in denim clothing, has become very desirable to a substantial proportion of the public. In addition to textile processing, cellulases are also known to be useful as animal feed additives, in the processing of pulp and paper and in the reduction of biomass.
A cellulase system derived from the thermophilic, filamentous, soil bacterium Thermomonospora fusca has been detected and the biochemical characteristics of that system and components thereof studied (Wilson, Critical Reviews in Biotechnology, Vol. 121/2, pp. 45-63 (1992)). One specific endoglucanase component of the T. fusca system, E5, has been sequenced (Lao et al., J. Bacter., Vol. 173, pp. 3397-3407 (1991)), and its disulfide arrangement and functional domains described (McGinnis et al., Biochemistry, Vol. 32, pp. 8157-8161 (1993)). McGinnis discloses that E5 treated with protease from Streptomyces lividans results in a 14 kD cellulose binding domain and a catalytically active 32 kD fragment which had lost the ability to bind to cellulose. Pure catalytically active S. lividans protease treated E5 was shown to have similar activity to intact enzyme on CMC. However, mixtures of catalytically active E5 fragments, when combined with intact E3 from T. fusca or intact E3 and CBHI from Trichoderma reesei, showed decreased performance to similar mixtures containing intact E5 instead of the fragment (PCT Publication No. 96/00281).
Despite intensive research related to the use of cellulases in industrial processes, cellulases known and used in the art often show significant drawbacks. For example, many cellulases have been problematic due to low activity in detergents. Surprisingly, Applicants herein have discovered that a mutant E5 cellulase comprises characteristics particularly desirable in certain industrial applications compared to wild type E5.